This application claims the priority of German patent document 103 04 530.9, filed Feb. 4, 2003 (PCT International Application No. PCT/DE2004/000162, filed Feb. 3, 2004) the disclosure of which is expressly incorporated by reference herein.
The present invention relates a deformable aerodynamic profile member.
Various arrangements and methods are known for adjusting and optimizing the buoyancy and flow resistance of a body with flow around it (e.g., in the form of an aerodynamic profile), to adapt to various ambient conditions. Such aerodynamic profiles may include, for example, helicopter rotor blades, aircraft wings or turbine blades, to name but a few examples.
In the field of aeronautical engineering, deformation of a profile curvature of such aerodynamic profiled members has been achieved mechanically by using different adjustment devices. However, gaps and hollow spaces then usually occur in the shell of the profile, which is a disadvantage for many applications.
To counteract this problem, German patent document DE 196 43 222 C2 discloses an arrangement in which the properties of flow around a body are modified by continuous deformation of an aerodynamic profile having an elastically deformable shell, using an adjustment device integrated into the profile.
German patent document DE 197 09 917 C1, on the other hand, describes a device for controlled deformation of a shell structure, having a number of bulging ribs, which are joined together by actuators to achieve a change in the curvature of an elastic component connected to the bulging ribs.
In addition, composite structures for producing and detecting deformation are known which have a plurality of piezoelectric fibers running in parallel (for example, U.S. Pat. Nos. 5,869,189 and 6,048,622). However, such fibers are very expensive, and are relatively inefficient due to their great weight. Furthermore, suitable contacting of the piezoelectric fibers is necessary. Another factor to be taken into account is achieving the most homogeneous possible field distribution, which is necessary for producing the piezoelectric effect. The electrodes required for this purpose may be provided, for example, by separate layers (i.e., electrode layers), which can be integrated into the composite structure only with a corresponding extra technical expense.
When using this known composite structure to induce deformation, it is also a disadvantage that as a rule a high voltage is necessary to trigger the piezoelectric fibers. This means that a high energy demand is generated, which makes the arrangement inefficient, and that a complex electronic control system is necessary. In addition, suitable safety provisions must be taken.
It is thus an object of the present invention to create a deformable aerodynamic profile whose profile curvature can be varied in a technically simple and effective manner.
This and other objects and advantages are achieved by the aerodynamic profiled member according to the invention, which has a front profile area, and a rear profile area situated in the downflow. The profiled member is bounded by shells on a pressure side and on a suction side, which converge at a rear edge of the profile. According to the invention, the profiled member is equipped with d33 piezo actuators in at least some locations for its deformation, such that their change in length occurs essentially in the direction of the planes of the shells when acted upon by electricity.
Because the so-called longitudinal (d33) effect (in which the change in length of the piezoelectric material takes place in the direction of the electric field) is known to be greater than the usual (d31) piezo effect (in which the change in length is perpendicular to the electric field), a more effective introduction of forces into the aerodynamic profile is possible by an appropriate alignment of piezoelectric actuators.
It is especially expedient to arrange the d33 piezo actuators on the pressure side and/or suction side of the shell. The shells are usually made of conventional construction materials and the d33 piezo actuators are attached, for example, by adhesive bonding. However, mechanical fastening means such as clamping devices or screwing devices may also be used for this purpose. In addition, the shell provided with the piezo actuators may also be provided with a protective layer to protect the piezo actuators from impact, pressure, pulling or other external influences (including environmental factors).
According to another embodiment, the d33 piezo actuators are integrated into the shell on the pressure side and/or suction side. This configuration is preferred in so-called composite structures, which may be metallic, but may also be so-called MMCs (metal matrix composites). Likewise, the d33 piezo actuators may be integrated into composite fiber structures. One advantage of this arrangement is that the piezo actuators are automatically protected.
Similarly, the invention may also be applied to other floating bodies, which are attached with an articulated joint to the aerodynamic profile, such as control flaps. In this case the control flap is provided with d33 piezo actuators which are aligned so that their change in length takes place essentially in the plane of the flap when exposed to an electric current in a similar manner. A design in which the flap with d33 piezo actuators is connected to the rear profile edge of the aerodynamic profile with an articulated connection is particularly advantageous.
It is especially advantageous for the d33 piezo actuators to be used in the form of stacks of piezoelectric elements (so-called piezo stacks or “laminar” piezo actuators) which have a laminar structure with alternating electrode layers and layers of piezoelectric material. This arrangement has the advantage that the electrodes are integrated into the piezo actuator, which greatly facilitates contacting of the piezo actuator and at the same time ensures a homogeneous field distribution within the piezo actuator. It is especially expedient that the electric field for inducing the d33 effect is supplied via the electrodes integrated into the laminar piezo actuator. The invention can therefore be implemented especially effectively and in a technically simple manner.
Furthermore, it is expedient for the laminar d33 piezo actuators to have a low thickness (approx. 0.5 to 2.5 mm) so that they have hardly any influence at all on the flow conditions. It is advantageous that such thin-layered d33 piezo actuators can be introduced or integrated easily into the shells of aerodynamic profiles, and have a low weight.
Furthermore it is expedient that the side dimensions of the d33 piezo actuators are between 5 and 60 mm. This permits easy adaptation to given geometries (e.g., corners, edges, rounded shapes, etc.).
The invention can be used, for example, in helicopter rotor blades, aircraft wings, turbine blades or the like.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.